Glue-guns comprise apparatus for the melting, dispensing and application of thermoplastic material usually supplied in the form of a rod. Examples of apparatus of this kind manufactured and sold by the applicants are described in U.K. Pat. No. 1 402 648, EPA No. 017 0487 (from UK application No. 84 19 302) and EPA No. 017 0488 (from UK application No. 84 19 303).
Such apparatus may be described as having a melt body providing a melt chamber in which thermoplastic material is melted, an inlet for a rod of thermoplastic material and an outlet comprising an orifice for dispensing and applying melted material, and means for heating the melt body so that thermoplastic material fed as a rod into the melt chamber may be melted and then dispensed and applied in molten condition from the orifice. Such apparatus finds use in various fields of application, commonly in the form of applicators for hot-melt adhesives and sealants and especially in hot-melt glue-guns having provision for feeding a rod of adhesive material to the melt body.
The present invention is concerned with hot-melt guns for melting rods of thermoplastic material, and for dispensing and applying the resulting hot-melt compositions and is more particularly concerned with a hand-held glue-gun comprising improved feeding means adapted to feed hot-melt material in the form of a rod to the melt body.
Rod feeding means employed in hand-held glue-guns often includes a trigger and associated mechanism arranged to grip a rod of thermoplastic material to be fed, and to advance it towards the melt chamber. In most cases, an inlet sleeve e.g. of heat-resistant, usually resilient, material is provided at the entrance to the melt chamber which is intended to assist in guiding the rod into the melt chamber and also to grip the surface of the rod as it is fed into the melt chamber thus minimising flow-back of melted material from the melt chamber inlet. For example, patent specification GB Pat. No. 1 402 648 (Bostik) describes a hand-held hot-melt glue-gun having feeding means for feeding a rod of hot-melt material in solid form through such an inlet sleeve into a melt body.
Glue-guns with such sleeves have indeed become commonplace and are described in many patent specifications such as GB Pat. No. 2 048 126 (Hilti).
However, outflow of melted rod from the inlet of a melt chamber can increase adversely if the temperature of the sleeve, which is in direct contact with the melt, rises so that the rod is softened or even prematurely melted, thus allowing unwanted egress of melt between the rod and the sleeve.
Various attempts have been made to improve the performance of such sleeves. For example, in GB Pat. No. 2 032 303 (Hilti) an insulating ring is interposed between the sealing sleeve and the melt chamber. GB Pat. No. 1 222 258 (Daubert) proposes the use of an insulating liner and EP No. 30 893 (Soc. Fr. d'Agrafage) makes use of a bush of heat-resistant material. None of these references however, propose to insert a further thermal barrier within the sealing sleeve itself.
It is an object of the present invention to provide a hot-melt dispenser comprising a sleeve which inhibits heat distortion of a rod of thermoplastic material fed to the melt.
It is a further object of the present invention to provide a sleeve for the inlet of a hot-melt dispenser or glue-gun which inhibits heat distortion of a rod of thermoplastic material held within said sleeve.